Signal transmission system



Feb. 25, 1 947. H. G. BUSIGNIES I 2,416,286

SIGNAL TRANSMISSION SYSTEM I Filed 001;. 7, 1942 2 Sheets-Shqefl nsManuLnm? DETECTOR g JFIER RECEIVER n/vp RESHHPER mm M00.

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' v SIGNAL TRANSMISSION SYSTEM Filed' Oct. '7, 1942 2 sheets-sheet 2 v F 81+ J INVENTOR. HEN/Pl G; BUS/GN/ES ATTORNEY Patented Feb. 25, 1947 SIGNAL TRANSMISSION SYSTEM Henri G. Busignies, Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation, a

corporation of Delaware Application October 7, 1942, Serial No. 461,143

18 Claims.

This invention relates to radio receiving systems and more particularly to time modulated impulse receivers.

For purposes of power economy and other uses, transmission of signals by time modulated impulses has been resorted to as described in U. S. patents to A. Reeves Nos. 2,266,401 and 2,256,336 and U. S. patent to E. Deloraine and A. Reeves No. 2,262,838. By the use of these pulse systems, either single pulses variable in length or pairs of pulses adjusted in time with respect to one another, it is possible to transmit and receive energy provided only that the spacing or length of the pulses is controlled in time in accordance with the modulating signal.

It has been proposed in pulse modulation systems to provide receivers in which a relatively simple tuned filter circuit is provided to convert the time modulated pulses into amplitude modulated signals so that they may be audibly reproduced. Such systems are described more fully in the application of E. Deloraine and E. Labin entitled Pulse transmission system, Serial No. 425,108, filed December 31, 1941, and the application of Ev Labin entitled Radio receiver, Serial No. 449,595, filed July 3, 1942. This sys tem works very satisfactorily but requires a relatively constant recurrence interval between the time modulated pulse pairs since the harmonic content of the wave and its variations. must be properly controlled. I

It is an object of my invention to provide a system for converting pulse modulation into amplitude modulation in accordance with the duration of a pulse formation without any interdependence upon the recurrence frequency of the pulse formations.

According to a feature of my invention, the object outlined above and others are accomplished by providing means responsive to the received pulse formations for producing wave trains of a given frequency and an amplitude dependent upon the duration of the pulse formation and further means for terminating the wave trains prior to the reception of the succeeding pulse formation.

A better understanding of my invention and the objects and features thereof may be had from the particular description thereof made with reference tothe accompanying drawingsin which-- Fig. l is a block diagram of a receiver embodying the features of my invention;

Fig. 2 is a set of curves used to explain the operation of the receiver in accordance with my invention;

Fig; 3 is a circuit diagram of a tuned oscillating circuit which may be part of the circuit of Fig.1;

Fig. 4 is a modified tuned oscillating qcircuit system which may be part of the system of Fig. 1; and Fig. 5 is a set of curves used to explain further features of my invention.

In Fig.1, a receiver element 10 is provided for receiving and amplifying pulse modulation signals in the manner of the usual R. F. and I. F. stages. Thesepulse modulation signals may be passed to demodulator and reshaper circuit H and from there passed to a tuned oscillation circuit l2 preferably a shock excited circuit which is provided with means such as the inherent damping of the circuit for terminating the produced wave prior to the reception of the succeeding group of pulses. The waves produced in tuned circuit l2 are then detected in a detector amplifier circuit I3 and applied to headphones M. In the event that amplitude modulationof the pulses is present as well as time modulation thereof, an auxiliary amplitude modulation detector amplifier I5 may be provided with suitable translating apparatus l6. I 1 In accordance with my invention the wave trains produced in the tuned oscillating circuit [2 are given amplitude characteristics dependent upon the spacing of the received pulse formations but substantially independent of the recurrence frequency of these pulse formations; A better understanding of the operation of the receiver may be had from the following description made with reference to Fig. 2. In this figure, curve A represents pulse formations which are produced in a known manner in the output of demodulator reshaper II in response to pulse signals received at H]. These pulses may be substantially square wave formations as shown in curve A for the most efficient operation. It should be understood, however, that the system described is operative for other pulse formations as well. Pulses 20 and 21 form one pulse formation and pulses 22 and 23 correspond to the succeeding pair of pulses'of the chain of received signal pulses have been reshaped, the recurrence period R of the pulse formations may be any desired amount. For example, this period R. may be varied from 39 to microseconds, this variation, of course, being controlled at the source of the signal pulses. Pulses 20 and 2| are controlled in width at l l and in the present instance may be considered as being one half a mircrosecond in width. The intervalbetween the two pulses which as measured between leading edges thereof is indicated as P varies according to the intelligence with which the received signal pulses are modulated." When pulse 2'0 is applied to the shock excited tuned 'cir'cuit, it immediately produces therein "a waveformation' shown"at- 30, curve B. The circuit is tuned to one'megacycle frequency so that one alternate or half a wavelength of the-wave produced in the circuit will occur duringthe pulse width pe'ri'od D. By

choosing this particular frequency, the leading a stronger oscillation. In one extreme position of modulation as illustrated in the solid line pulse 2!, this pulse when applied. to .the same shock excited circuit tends to produc'e'an oscillation 180 out of phase with theoscillationproduced by pulse as shownvby the light line curve 3|. This pulse accordingly serves to modify wave and substantially kills the oscils lation producing the resultant wave shown in the heavy line curve 3.2.

Upon modulation of the pulsesin time, pulses 20 and 2-! move toward one another asshown by therdotte'd lines 44 and of curve A. Accordingly, the successive eifects ofpulses!!!) and 2|. on* tuned circuit :2 is nolonger such as to completely' damp out the Wave buttends to-produce two wave formations and 4 i as'shown in curve C which together produce-the resultantcurveAZ shown in heavy lines in curve C.

Curves B' and C may be considered as. representing the extreme modulation positions of pulses 20 and 2!. For intermediate modulation positions of pulses 2i! and 21 there will be produced wavev trains of varying amplitude in accordance with the variation in spacing of the modulated pulses. Accordingly, when these successively producedwave trains are detected'at It, the. modulation envelope of the time modulated pulseswill be reproduced. This, envelope may be further; amplified, ifnecessary,v and applied directly to headphones or a. loudspeaker or any other desired translatingdevice.

It can thus be seen that the-successively received pulse formations serve to produce wave trains varying in amplitude in accordance with the duration of the'pulse formation interval independently ofthe recurrencefrequency R between thepulses. However, in order toassure that there is no" interaction between successively received pulserfor-mations; it is desirable that the tuned oscillating circuit be controlled so that the wave formations produced thereindo not endure for a period greater than the time spacing" of these pulse formations. This may simply be accomplished by having tuned circuit [2 of such damp- 3 ing' characteristics as to reduce the waves substantially to zero prior to the initiation of new from demodulator H is applied to the input grid 63 of vacuum tube 68 across the anode 64 and cathode 65 of which is connected atuned circuit comprising an inductance 6i and condenser 52. This tuned circuit is adjusted to have the proper frequency and to have sufficient damping to reduce the waves generated substantially to zero before a second pulse formation is applied thereto. The output circuit connected across the tuned circuitl may then be applied directly to the detector arrangement i3 as shown in Fig. i.

The curves shown in Fig. 2 are all shown as being, highly damped to assure termination of the wave trains at a desired interval. In some cases, however, it may be preferable to use a tuned circuit which is nothighly damped and toprovide means for terminating oscillation of this circuit at a. desired period after the reception of pulses. By using the higher Q tuned circuit, greater amplitude of thereceived signals will be assured and the system therefore will be more sensitive to-the reception of signals.

A suitable arrangement for accomplishing this result is illustrated in Fig. 4 which shows a paroscillations bythe succeeding received pulse formation. This action is indicated by the dotted 1 triangles 33; 33' shown in curves B and C respectively.

When square wavessuch as 2i] and 21 are proit is clear that only the odd harmonics will be duced in the demodulator and reshaping circuit,

Waves the'tuned circuitmust be properly related to one ofthese harmonic frequencies. Thus the 1 frequency must bechosen so that;

in the above equationchosen-as 2, the wave formationsproduced by pulses 26 and 2i in, their successive; positions may be in the form; shown in. curves Diand-Erespectivelyof: Fig. 2.

A-rsuitable-iform tot tunedoscillating circuit for operatinggto: produce the: wave formations shown in: Fig.2: is; illustrated; in more detail in Fig. 3'.

In this figure;;the*-tuned: oscillating circuit l2v is shown generally in broken lines. The output Y the circuit supplying the pulses to tube H.

' ticular circuit arrangement for tuned oscillating circuit i2. In this case, pulses 20 and 2| are applied over a delay line Iii to a vacuum tube 60. In the output of vacuum tube 5%] is provided tuned circuit 6!, 52-corresponding to the similar tube and circuit arrangement of Fig. 3.1 However, the tuned circuit is here adjusted to have very low losses so that the oscillations-will tend to-persist for a long period of time. Across tuned circuit ii! 62 is connected the anode l3 and cathode 74 of a; variable impedance tube '5 I. When no energy is applied to-the grid E5 of this tube, the impedance is substantially thatof an open circuit so that no substantial damping of the tuned circuit will occur. I providefurthera connection '56 from theinput of circuit i2'to the grid ?5 of tube l'i so that the received pulses will be applied to this tube causing it to be conductive and thoroughly damping any oscillations in tuned circuit BI, 62; The delay line iii is-made of sufflcient length to permit passage of these pulses from the grid of tube 'il prior tothe application of the pulses 'to the tuned circuit over tube 68.

Thus the pulses first are applied to the grid of tube H overtime constant circuit "l2, which includes condenser 71 and resistor '18, causing a damping of any oscillations in the circuit. Then these pulses are successively applied to the tuned circuit to produce the desired wave train. This wave train then persists for a period of time until the succeeding pulse formation reaches the receiver. These succeeding pulses are i l-- mediately applied to tube H damping out all signs of oscillation from circuit El, 62 after which this,

the length of the delay period may be controlled at will. It should, be also clear that instead of putting the delay line in the input circuit of the tuned circuit, the delay line could be placed in In this case, the period would be such as to terminate produced oscillations at a fixed time after arrival. ofthe pulses instead. of a fixed time prior to application of thezsucceeding pulses. This latter system, however, is generally less desirable sinceitrequires a much longer delay. period. for the pulse. I

In general, the system as described above wherein the pulses are varied in spacing with respect to one another is preferred, but the principles of my invention apply also to other types of pulse modulation systems. For example, the type of pulse modulation system wherein one of the pulses is fixed in time and the other one is varied in accordance with the modulation, is illustrated in curves J and K. of Fig. 5. Curve J illustrate the fixed pulse 80 and variable pulse 8| shown in solid and dotted lines respectively to indicate two modulation positions. Pulse 8| in its solid line position in cooperation with pulse 80 will produce the solid line curve 82 of curve K while in the dotted line position it will produce a wave corresponding to the dottedline 83 of curve K. When this type of modulation is used. it is necessary only to transm t the variable pulse since the fixed pulse may then be locally reproduced at the receiver. However, in accordance with my system, it is generally preferable to transmit both pulses since otherwise the recurrence freouency would have to be maintained relatively stable in order that the locally produced pul e could be properly timed.

Another form of pulse modulation comprises the product on of long pulses, the variation in len th of wh ch serves to indicate thetime modulation. Such type of waves may also be used with a receiver embodying the principles of my shown at M. In the full line position, the leading edge of pulse 90 tends to produce an oscillation in the shock excited circuit while the trailing edge of the pulse serves to modify the amplitude of this wave. Thus in the solid line position, the pulse will produce a solid line curve 92 shown in curve M while in the dotted line position, the dotted curve 93 will be produced.

In all of the above described systems, the operation has been illustrated in connection with pulses which have relatively straight leading and trailing edges. The principles ofmy invention, however, may be readily applied to any form of pulse system regardless of the particular shape thereof. Accordingly, it is not necessary to reshape the received pulses but it is entirely possible to merely demodulate them before applying them to the tuned circuit. Curves N and O of Fig. 5 serve to illustrate pulses of this general nature. In curve N there are shown two pulses 25 and 26 roughly corresponding in spacing to pairs of pulses such as shown at and 2 I. Each of these pulses, however, has a very sharp leading edge and a relatively sloping trailing edge. When pulse is applied to the tuned oscillating circuit, the leading edge will tend to-prcduce oscillations therein. The trailing edge will tend to produce oscillations in the opposite direction but since the trailing edge is much less steep than is the leading edge, the harmonic content thereof is much less so that this edge will serve'only to reduce the amplitude of the produced oscillations but will not cause extinction thereof. Similarly, the leading edge of pulses 25 will also serve to produce oscillations serving to modify those produced by the leading edge of pulse 25. When this type of pulse is used, then the harmonic frequency need not be limited to the odd harmonics as in the case of the square wave pulses. Accordingly, the two pulses 25 and 28 may serve to produce an to utilize pulses transmitted so that this is not" the case. If the repetition period R is so adjusted so as to produce no resulting oscillation in the receiver in the absence of modulation, the oscillations produced in the tuned circuit will be such that the output signal will be similar to the side bands without any carrier, as inordinary suppressed carrier audio-modulation signalling. In such case, it is necessary to supply locally the carrier oscillations prior to detection in order that the envelope may be properly reproduced. I

It will also be understood that while it is preferable to have one extreme of modulation produce substantially no output energy, the system will be readily operable if this extreme of modulation is chosen to produce a maximum of energization of the oscillating circuit. In this latter case, variation of the pulse spacing will reduce the amplitude in accordance with the modulations instead of increasing it as in the given example. In general, this system, however, is not preferred since it is not as efficient as the system outlined in the specific examples.

The receiving system in accordance with my invention is readily operable for reception of pulses regardless of the recurrence period as stated above. Accordingly, means may be provided at the transmitter for continuously varying this recurrence period. With such variation of recurrence, it is much more diflicult for an unauthorizedperson to intercept and translate the message or to produce jamming, pulses to obliterate the indication.

While I have described above the principles of amplitude of said produced wave train in accordance with the termination of said periods, means for substantially terminating each pro- .duced wave train prior to initiation of the succeeding wave train, andmeans for detecting said produced wave trains to obtain said modulating envelope.

2. A. receiving system according to claim 1 wherein said pulse formations representing periods of time comprise pairs of pulses variably, displaced with respect to one another, and said first named means comprises a shock excited tuned circuitand means for applying said pulses thereto.

3. A receiving system according to claim l wherein said first named means comprises ashock excited tuned circuit, and said second named means comprises the inherent damping characteristics of said tuned circuit.

4. A receiving system for receiving time modulated pulse energy in which the signal amplitudes are represented by the relative time dising each of said wave trains prior to the production of the succeeding wave train, and means for detecting said wave trains to produce the module.

tion envelope of said received energy. 7

5. A receiver for producing the modulation envelope offa received wave, said wave comprising a seriesof pairs of pulses of radio frequency controlled in time position in accordance with a modulating wave, comprising means for receiving and reshaping said pulses, a shock excitation oscillatory circuit, means for causing excitation of said circuit to produce a wave train of a given frequency in response to reception of the first pulse of said pair, means responsive to the second pulse of said pair for modifying the amplitude of said wave train in accordance with the time position of said second pulse, means for substantially terminating said wave train prior to reception of the succeeding, pulse pair, and means for detecting said modified wave trains to reproduce said modulation envelope. I

6. A receiver according to claim wherein said means for terminating said modified wave trains comprises the inherent damping characteristics of said circuit. 7

'7. A receiver according to claim 5-wherein said means for terminatingsaid modified wave trains comprises, normall high impedance means connected across said circuit, and means responsive to received signals for effectively lowering the impedance of said normally high impedance wavetrains, and delay means for producing a'relative time delay between application of said pulse formations to said respective circuit means.

10. A receiver according to claim 9 wherein said pulse formations each comp-rise a pair of pulses, said first named circuit means comprising a tuned circuit shock excited into oscillation by the first pulse of said pairs to produce Wave trains and excited by the second pulse of said pair to modify the produced wave trains in accordance with the spacing of said pulses.

11. A receiver according to claim 9 wherein said pulse formations each comprise a pair of pulses, said first named circuit means comprising a tuned circuit shock excited into oscillation by the first pulse of said pairs to produce waves forming said trains and excited by the second pulse of said pair to modify the produced wavesin accordance with the spacing of said pulses, and saidsecond named circuit means comprise a variable impedance shunt connected across said tuned circuit, and s means in said shunt connection for reducing said impedance in response to said applied pulse formations. 7

12. A receiver according to claim '9, further file of this patent:

comprising detector means for detecting said generated terminated wave trains to produce the envelope frequencies of said series of pulse formations.

13. A receiver according to claim 9 wherein said pulse formations each comprise apair of pulses, said first named circuit means comprising a tuned circuit shock excited into oscillation by the first pulse of said pairs to produce a wave train and excited by the second pulse of said pair to modify the produced wave trains in accordance with the spacing of said pulses, further comprising detector means for detectingsaid generated terminated wave trains to produce the envelope frequencies of said series of pulse formations.

14. A receiver according to claim 9 wherein said pulse formations each comprise a pair of pulses, said first named circuit means comprising a tuned circuit shock excited into oscillation by the first pulse of said pairs to produce wave trains and excited by the second pulse of said pair to modify the produced wave trains in accordance with the spacing of said pulses, and said second named circuit means comprise a variable impedance shunt connected across said tuned circuit, and means in said shunt connection for reducing said impedance in response to said applied pulse formations, further comprising detector means for detecting said generated terminated wave trains to produce the envelope frequencies of said series of pulse formations. 1

' 15. In a receiving system for receiving trains of pulse formations representing variable pe-.

riods of time in accordance with a modulating envelope, means for producing wave trains representing the initiation of said periods, and means for modifying the amplitude of the produced wave trains in accordance with the termination of said periods.

18. In a receiving system for receiving trains of pulse formations representing variable periods of time in accordance with a modulating envelope, means for producing wave trains representing'the initiation of said periods, means for modifying the amplitude of the produced Wave trains in accordance with the termination of said periods, and means for detecting the produced wave trains to obtain said modulating envelope.

1?. In a receiving system for receiving trains of pulse formations representing variable periods of time in accordance with a modulating envelope,-

the method of demodulating the time modulaticn of said pulses'comprising producing wave trains each representing the initiation of one of said perioda and modifying the amplitude of each 'wave tra n by the termination of the corresponding period. a

18. A method according to claim 17 further inc uding the'step of substantially terminating each of said wave trains prior to initiation of the succeeding wavetrain. V

V HENRI G. BUSIGNIES.

REFERENCES CITED The following references are of record in the v UNITED STATES PATENTS 

